1. Field of the Invention
The present invention relates to rapid thermal processing (RTP) of semiconductor wafers and, more particularly, to a radiation-first RTP method for uniformly thermal-processing a rotating semiconductor wafer.
2. Description of the Prior Art
Rapid thermal processing (hereinafter referred to as “RTP”) methods and RTP systems are known in the art. A RTP chamber refers to a device that rapidly heats objects, such as semiconductor wafers. Such devices typically include a substrate holder for holding a semiconductor wafer and an energy source for heating the wafer. During heat treatment, the semiconductor wafers are heated under controlled conditions according to a pre-set temperature regime. For monitoring the temperature of the semiconductor wafer during heat treatment, thermal processing chambers also include radiation sensor devices, such as pyrometers, that sense the radiation being emitted by the semiconductor wafer at a selected wavelength. By sensing the thermal radiation being emitted by the wafer, the temperature of the wafer can be calculated with reasonable accuracy.
The thrust of the work was increasing the temperature uniformity, and developing heating cycles and processes which decreased the thermal budget. Prior art RTP chambers can heat unstructured, homogeneous materials in the form of a flat plate or disk, and produce temperature uniformities across the plate adequate for semiconductor processing processes.
The wafers are generally inserted into a chamber with at least some portions of the chamber walls transparent to transmit radiation from powerful heating lamps. These lamps are generally tungsten-halogen lamps, but arc lamps or any other source of visible and/or near infrared radiation may be used. The radiation from the lamps is directed through the transparent portions of the walls on to the surface of the wafer to be heated.
FIG. 1 shows a cross-sectional sketch of a prior art RTP chamber 10 with a wafer 12 supported by quartz pins 14 in position for heating by radiation from a set of lamps 16 and 18. The chamber 10 is supported by a housing 20 having highly polished interior walls 22. A door 24 is used to make a gas tight seal for the chamber 10. The temperature of the wafer 10 is measured by a pyrometer 26. A computer 32 receives the temperature reading from the pyrometer 26, and controls the lamps 16 and 18 to heat the wafer 12 according to a preprogrammed schedule. The computer 32 also serves to control a gas flow controller 30, which introduces process gas 28 into the chamber 10.
Rotation of susceptors bearing wafers is well known as a means of ensuring uniform heating and growth of films in semiconductor processes. FIG. 2 depicts a flow chart according to a prior art RTP method. After loading the wafer into the cooled down RTP chamber (Step 42), the wafer, which is supported by the quartz pins and has a temperature (typically room temperature) that is lower than the chamber walls that are just cooled down to about 30–80° C., starts to rotate (Step 44). Processing gas, if necessary, is then flowed into the chamber (Step 46). A pre-set heating program, which is stored in and executed by the computer, is then activated to heat the wafer in either a soak mode or a spike mode for a pre-selected time period (Step 48). However, the prior art method for thermal processing a wafer arises particle problems.